Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia

In this paper we study the polymetamorphic processes of very low-grade metamorphism (VLGM) in subgreenschists facies to low-grade metamorphism (LGM) affecting the calcalkaline volcanic sequence of Middle or Upper Jurassic/Lower Cretaceous age in the North Patagonian Andes (Lat 42°30′-43° S), south o...

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Autores principales:	Vattuone de Ponti, María Elena, Latorre, Carlos Oscar, Leal, Pablo Rodrigo
Publicado:	2005
Materias:	Argentina Chubut Low-grade metamorphism Patagonia Polymetamorphism Very low-grade metamorphism
Acceso en línea:	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10268774_v22_n3_p315_Vattuone http://hdl.handle.net/20.500.12110/paper_10268774_v22_n3_p315_Vattuone
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	paper:paper_10268774_v22_n3_p315_Vattuone
record_format	dspace
spelling	paper:paper_10268774_v22_n3_p315_Vattuone2023-06-08T16:00:15Z Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia Vattuone de Ponti, María Elena Latorre, Carlos Oscar Leal, Pablo Rodrigo Argentina Chubut Low-grade metamorphism Patagonia Polymetamorphism Very low-grade metamorphism In this paper we study the polymetamorphic processes of very low-grade metamorphism (VLGM) in subgreenschists facies to low-grade metamorphism (LGM) affecting the calcalkaline volcanic sequence of Middle or Upper Jurassic/Lower Cretaceous age in the North Patagonian Andes (Lat 42°30′-43° S), south of the Cholila locality, Chubut Province, Argentinian Patagonia. The sequence, deposited in marginal basins, is intruded by granitic rocks of Early Cretaceous age. The protolith is basaltic and andesitic in composition; the secondary minerals were deposited replacing the matrix, phenocrysts, infilling veins and amygdales. Three metamorphic processes are recognized. The first regional process that affected the sequence occurred in a non- deformational environment of extensional type, with moderate to steep thermal gradient, and high fO2. In this first stage, greenschists-facies temperatures of >300 °C at 2 kb are indicated by the observed assemblage of epidote-chlorite-actinolite-albite-quartz-magnetite-titanite+grandite (without pumpellyite nor prehnite), which formed at high XCO2/XH2O. Temperature and pressure then decreased to subgreenschists facies of VLGM in pumpellyite-actinolite facies with assemblages of pumpellyite-actinolite-epidote (without prehnite) and in prehnite-pumpellyite facies (with epidote-chlorite-albite-quartz-pumpellyite±prehnite). In the northern area, the assemblage epidote, albite, chlorite, adularia, laumontite and scarce pumpellyite and prehnite indicates the zeolite facies. Nearer to Cholila locality, there is evidence of a second stage of VLGM, probably related to the inversion of previous faults and to the uplift of the area in Upper Cretaceous times; the increased temperatures in this stage were generated by fluids related to magmatism. The presence of wairakite and yugawaralite together with laumontite is in accordance with a geothermal-type VLGM in the high-temperature zeolite facies. The equilibrium assemblage wairakite-yugawaralite-laumontite indicates P-T conditions of <220 °C and <0.5 kb. In the first two processes, the neutral to slightly alkaline hydrothermal fluids, the high PH2O/ Ptotal ratio, and the high fO2 conditions in the stability field of hematite, favored the formation of calcsilicates and calcic zeolites. Later, new fractures affected the rocks and facilitated the circulation of new, more alkaline fluids; in some areas, fluids with acidic pH promoted the formation of illite and sericite, but at neutral pH, barrerite, offretite and smectite were deposited in amygdales at temperatures below 180 °C. Fil:Vattuone, M.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Latorre, C.O. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Leal, P.R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2005 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10268774_v22_n3_p315_Vattuone http://hdl.handle.net/20.500.12110/paper_10268774_v22_n3_p315_Vattuone
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Argentina Chubut Low-grade metamorphism Patagonia Polymetamorphism Very low-grade metamorphism
spellingShingle	Argentina Chubut Low-grade metamorphism Patagonia Polymetamorphism Very low-grade metamorphism Vattuone de Ponti, María Elena Latorre, Carlos Oscar Leal, Pablo Rodrigo Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia
topic_facet	Argentina Chubut Low-grade metamorphism Patagonia Polymetamorphism Very low-grade metamorphism
description	In this paper we study the polymetamorphic processes of very low-grade metamorphism (VLGM) in subgreenschists facies to low-grade metamorphism (LGM) affecting the calcalkaline volcanic sequence of Middle or Upper Jurassic/Lower Cretaceous age in the North Patagonian Andes (Lat 42°30′-43° S), south of the Cholila locality, Chubut Province, Argentinian Patagonia. The sequence, deposited in marginal basins, is intruded by granitic rocks of Early Cretaceous age. The protolith is basaltic and andesitic in composition; the secondary minerals were deposited replacing the matrix, phenocrysts, infilling veins and amygdales. Three metamorphic processes are recognized. The first regional process that affected the sequence occurred in a non- deformational environment of extensional type, with moderate to steep thermal gradient, and high fO2. In this first stage, greenschists-facies temperatures of >300 °C at 2 kb are indicated by the observed assemblage of epidote-chlorite-actinolite-albite-quartz-magnetite-titanite+grandite (without pumpellyite nor prehnite), which formed at high XCO2/XH2O. Temperature and pressure then decreased to subgreenschists facies of VLGM in pumpellyite-actinolite facies with assemblages of pumpellyite-actinolite-epidote (without prehnite) and in prehnite-pumpellyite facies (with epidote-chlorite-albite-quartz-pumpellyite±prehnite). In the northern area, the assemblage epidote, albite, chlorite, adularia, laumontite and scarce pumpellyite and prehnite indicates the zeolite facies. Nearer to Cholila locality, there is evidence of a second stage of VLGM, probably related to the inversion of previous faults and to the uplift of the area in Upper Cretaceous times; the increased temperatures in this stage were generated by fluids related to magmatism. The presence of wairakite and yugawaralite together with laumontite is in accordance with a geothermal-type VLGM in the high-temperature zeolite facies. The equilibrium assemblage wairakite-yugawaralite-laumontite indicates P-T conditions of <220 °C and <0.5 kb. In the first two processes, the neutral to slightly alkaline hydrothermal fluids, the high PH2O/ Ptotal ratio, and the high fO2 conditions in the stability field of hematite, favored the formation of calcsilicates and calcic zeolites. Later, new fractures affected the rocks and facilitated the circulation of new, more alkaline fluids; in some areas, fluids with acidic pH promoted the formation of illite and sericite, but at neutral pH, barrerite, offretite and smectite were deposited in amygdales at temperatures below 180 °C.
author	Vattuone de Ponti, María Elena Latorre, Carlos Oscar Leal, Pablo Rodrigo
author_facet	Vattuone de Ponti, María Elena Latorre, Carlos Oscar Leal, Pablo Rodrigo
author_sort	Vattuone de Ponti, María Elena
title	Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia
title_short	Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia
title_full	Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia
title_fullStr	Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia
title_full_unstemmed	Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia
title_sort	very low- to low-grade polimetamorphism in jurassic-cretaceous volcanic rocks to the south of cholila, chubut, argentinian patagonia
publishDate	2005
url	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10268774_v22_n3_p315_Vattuone http://hdl.handle.net/20.500.12110/paper_10268774_v22_n3_p315_Vattuone
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_version_	1768546357594816512

Very low- to low-grade polimetamorphism in Jurassic-Cretaceous volcanic rocks to the south of Cholila, Chubut, Argentinian Patagonia

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